What Makes a Great Party?

We like to celebrate our birthday in the most unassuming way possible: nice quiet dinner with only the closest friends. This year, however, we've unwittingly agreed to a full-on bash. It started out as a casual bbq and has become a last minute P-A-R-T-Y. But with just a few days to go, we still have NOTHING planned. It doesn't need to be fancy, just a bit more pulled-together than our usual camp chairs 'round the firepit deal. We're begging for help here: give us your best last-minute trick for making a party memorable and fun without breaking the bank!

What do you think are the key components of a good party? Good food? Music? Places to sit?